A variety of medical conditions have been treated by introducing an insertable medical device having a coating for release of a therapeutic agent. For example, various types of medical devices coated with a therapeutic agent, such as stents, have been proposed for localized delivery of such agents to a body lumen. See, e.g., U.S. Pat. No. 6,099,562 to Ding et al. issued on Aug. 8, 2000. However, it has been noted that therapeutic agent delivery by means of medical devices can be improved.
At present, many medical devices used for delivery a therapeutic agent to a body site are simply coated with a coating material, and may be fully encapsulated by the material. In the field of stents, the struts of the stent are typically sprayed with a polymer/therapeutic agent mix. There are, however, several drawbacks that may accompany full encapsulation of stent struts, including (1) an undue increase in effective stent strut profile; (2) the perhaps unwanted presence of a therapeutic agent on the inner surface (or subluminal surface) or strut side surfaces of the stent (where the agent may not provide a therapeutic benefit); (3) an increase in the likelihood that the total amount of therapeutic agent on the stent is greater than is needed (as a significant amount of the coating may simply serve to provide mechanical anchorage of the coating to the stent); (4) an increase in the balloon withdrawal forces because of friction between the balloon and the stent coating; and (5) the trade-offs that occur in selecting a therapeutic agent that is efficacious but durable.
Another approach used with medical devices for delivery of a therapeutic agent is to coat the stent abluminally, wherein the coating is applied only on the outer surface (or abluminal surface) of the device. In the field of stents, coatings on only the abluminal surface may also present drawbacks, however, including (1) the fact that very few effective coating methods are known which can enable deposition of precise quantities of coating on the abluminal surface of a stent; (2) precise coating methods are generally very time-consuming and may not lend themselves to commercial process scale-up; (3) as the success of abluminal coating may depend on the adhesion of the coating to the stent surface, this may unduly limit the range of materials that may be utilized; and (4) an undue increase in effective stent strut profile. Moreover, coating a stent abluminally may require the use of a polymer, which may be used to modulate therapeutic agent release over a period of time, but which may also have drawbacks relating to thrombosis concerns. However, coating a stent abluminally without the use of a polymer may result in a therapeutic agent release rate that is too high, and/or may result in ineffective coating adhesion to the stent.
Thus, there is a need for a medical device such as a stent with support elements that overcomes the above, and other, drawbacks.